At least some computer systems combine data from multiple sources into a single data stream in order to communicate over a single communications resource, such as an interface to a local or wide area network. Many such systems utilize techniques such as time-division multiplexing and framed data blocks to identify the source of the data as the data is merged into a single stream. But time division multiplexing results in unused bandwidth if a data source is inactive. Framed data blocks avoid the issue of unused bandwidth, but create a tradeoff between latency and bandwidth efficiency. The smaller the blocks, the lower the latency, but efficiency also becomes lower with smaller blocks as more bandwidth is used for identification information. If the blocks are made larger, efficiency is improved, but latency increases as some data sources must be buffered and the transmission of the buffered data delayed while blocks containing data from another source are transmitted.